Silicone rubber sponge composition, silicone rubber sponge, and process for making the sponge

ABSTRACT

A silicone rubber sponge composition, a silicone rubber sponge, and a process for making the silicone rubber sponge. The silicone rubber sponge composition comprises (A) 100 parts by weight organopolysiloxane gum described by average structural unit R a SiO (4−a)/2 , where R is a monovalent hydrocarbon group or haloalkyl and a is 1.8 to 2.3 and having a viscosity of 1,000,000 mPa·s or above at 25° C., (B) 1 to 400 parts by weight inorganic filler, (C) 0.01 to 50 parts by weight hollow thermoplastic resin particles, (D) 0.1 to 10 parts by weight liquid compound with a boiling point above room temperature, and (E) a curing agent in an amount sufficient to cure the composition.

FIELD OF THE INVENTION

The present invention relates to a silicone rubber sponge composition, asilicone rubber sponge, and a process for making the sponge. Moreparticularly, it relates to a silicone rubber sponge composition thatgives a silicone rubber sponge having fine, uniform cells, a siliconerubber sponge, and a process for making the silicone rubber sponge.

BACKGROUND OF THE INVENTION

Due to their outstanding heat and weather resistance and light weight,silicone rubber sponges are used for automotive parts, such as packings,gaskets, and O-rings; as sheath materials for rollers in copiers, and assealing materials of various kinds. A number of silicone rubber spongecompositions have been proposed to date. Patent Publication (Kokoku)44-461 and Unexamined Patent Application Laying Open 7-247436, forexample, teach silicone rubber sponge compositions containing thermallydecomposable organic blowing agents such as azobisisobutyronitrile.However, silicone rubber sponges produced from these compositions tendto have coarse cells, making it difficult to consistently producesilicone rubber sponges having fine, uniform cells. Accordingly, thereis a need for a silicone rubber sponge composition having finer cells.

It is an object of the present invention to provide a silicone rubbersponge composition that gives a silicone rubber sponge having fine,uniform cells, a silicone rubber sponge, and a process for production ofthe sponge.

SUMMARY OF THE INVENTION

The present invention relates to a silicone rubber sponge composition, asilicone rubber sponge, and a process for making the silicone rubbersponge. The silicone rubber sponge composition comprises (A) 100 partsby weight organopolysiloxane gum described by average structural unitR_(a)SiO_((4−a)/2), where R is a monovalent hydrocarbon group orhaloalkyl and a is 1.8 to 2.3 and having a viscosity of 1,000,000 mPa·sor above at 25° C., (B) 1 to 400 parts by weight inorganic filler, (C)0.01 to 50 parts by weight hollow thermoplastic resin particles, (D) 0.1to 10 parts by weight liquid compound with a boiling point above roomtemperature, and (E) a curing agent in an amount sufficient to cure thecomposition.

DESCRIPTION OF THE INVENTION

A first embodiment of the present invention is a silicone rubber spongecomposition comprising

(A) 100 parts by weight organopolysiloxane gum described by averagestructural unit R_(a)SiO_((4−a)/2), where R is a monovalent hydrocarbongroup or haloalkyl and a is 1.8 to 2.3 and having a viscosity of1,000,000 mPa·s or above at 25° C.,

(B) 1 to 400 parts by weight inorganic filler,

(C) 0.01 to 50 parts by weight hollow thermoplastic resin particles,

(D) 0.1 to 10 parts by weight liquid compound with a boiling point aboveroom temperature, and

(E) a curing agent in an amount sufficient to cure the composition.

A second embodiment of the present invention is a silicone rubber spongeproduced by heat curing of the silicone rubber sponge composition. Athird embodiment of the present invention is a process for production ofa silicone rubber sponge composition comprising the steps of combiningcomponents (A) and (B) to produce a silicone rubber base compound, andincorporating component s (C), (D), and (E) into the silicone rubberbase compound. A fourth embodiment of the present invention is a processfor production of a silicone rubber sponge comprising the step of curingthe composition by heating to a temperature equal to or above thesoftening point of the thermoplastic resin of component (C).

Component (A) is the principal component of the present composition. Itmust have a viscosity at 25° C. of 1,000,000 mPa·s or above, andpreferably 5,000,000 mPa·s or above. Since component (A) is a gum, itwill have Williams plasticity of 50 or greater, and preferably 100 orgreater. The degree of polymerization of component (A) is typically3,000 to 20,000, with the weight-average molecular weight being 20×10⁴or above. The class of compounds known as organopolysiloxane gums usedas principals in organic peroxide-curing millable compositions can beused for component (A). Component (A) consists of an organopolysiloxanegum described by the following average unit formula R_(a)SiO_((4−a)/2),where R is a monovalent hydrocarbon group or haloalkyl and a is 1.8 to2.3. Monovalent hydrocarbon groups represented by R include alkyls suchas methyl, ethyl, and propyl; alkenyls such as vinyl and allyl;cycloalkyls such as cyclohexyl; aralkyls such as β-phenylethyl; andaryls such as phenyl and tolyl. Haloalkyl groups represented by Rinclude 3,3,3-trifluoropropyl and 3-chloropropyl.

Where the curing agent consists of either an alkyl peroxide or aplatinum catalyst used concomitantly with a organopolysiloxanecontaining silicon-bonded hydrogen atoms, the organopolysiloxane gummolecule must have at least two silicon-bonded alkenyls. Alkenyl hererefers, for example, to vinyl, ally, propenyl, and hexenyl groups.Silicon-bonded organic groups other than alkenyl include alkyls such asmethyl, ethyl, and propyl; aryls such as phenyl and tolyl; andhaloalkyls such as 3,3,3-trifluoropropyl and 3-chloropropyl. Themolecular structure of component (A) may be linear or linear containingbranches. Component (A) may be a homopolymer, copolymer, or a blend ofpolymers. Specific examples of the siloxane units of component (A) aredimethylsiloxane, methylvinylsiloxane, methylphenylsiloxane, and(3,3,3-trifluoropropyl)methylsiloxane units. Examples of molecular chainterminal endgroups of component (A) are trimethylsiloxy,dimethylvinylsiloxy, methylvinylhydroxysiloxy, and dimethylhydroxysiloxygroups. Examples of such organopolysiloxane gums includemethylvinylpolysiloxane gum that is endblocked at both terminals withtrimethylsiloxy groups, a copolymer gum of methylvinylsiloxane anddimethylsiloxane that is endblocked at both terminals withtrimethylsiloxy groups, dimethylpolysiloxane gum that is endblocked atboth terminals with dimethylvinylsiloxy groups, a copolymer gum ofmethylvinylsiloxane and dimethylsiloxane that is endblocked at bothterminals with dimethylvinylsiloxy groups, a copolymer gum ofmethylvinylsiloxane and dimethylsiloxane that is endblocked at bothterminals with dimethylhydroxysiloxy groups, a copolymer gum ofmethylphenylsiloxane, methylvinylsiloxane, and dimethylsiloxane that isendblocked at both terminals with methylvinylhydroxysiloxy groups, and acopolymer gum of (3,3,3-trifluoropropyl)methylsiloxane,methylvinylsiloxane, and dimethylsiloxane that is endblocked at bothterminals with methylvinylhydroxysiloxy groups.

Examples of the inorganic filler of component (B) are reinforcingfillers such as finely divided silica (e.g. dry process silica or wetprocess silica) and finely divided silica whose surfaces have beentreated with an organochlorosilane, organoalkoxysilane,hexaorganodisilazane, organosiloxane oligomer, or the like; andsemi-reinforcing or extending fillers such as powdered quartz,diatomaceous earth, heavy calcium carbonate, light calcium carbonate,magnesium oxide, calcium silicate, mica, aluminum oxide, aluminumhydroxide, carbon black, and the like. In excessively large amounts,component (B) is difficult to incorporate into component (A) andaccordingly the range 1 to 400 parts by weight per 100 parts by weightof component (A) is preferred, preferably using from 1 to 100 parts byweight for the reinforcing fillers and from 1 to 150 parts by weight forthe semi-reinforcing or extending fillers.

The hollow thermoplastic resin particles used for component (C) serve asnuclei for cell formation, and also make cell distribution uniform. Anexemplary component (C) is a material consisting of thermoplastic resinshells having an inert gas enclosed therein. Thermoplastic resinsinclude silicone resins, acrylic resins, and polycarbonate resins. Inpreferred practice, the thermoplastic resin will have a softening pointof from 40 to 200° C., and especially 60 to 180° C. Inert gases includeair, nitrogen gas, helium gas, and the like. Component (C) averageparticle size is preferably within the range of 0.1 to 500 μm, and morepreferably 1 to 50 μm. Component (C) may be prepared, for example, byspraying an aqueous dispersion of a thermoplastic resin dissolved in asolvent from a spray nozzle into a heated air stream and evaporating theorganic solvent while granulating the thermoplastic resin. Component (C)is included in amounts of 0.01 to 50 parts by weight, preferably 0.1 to40 parts by weight, per 100 parts by weight of component (A).

Component (D), a liquid compound with a boiling point above roomtemperature, is an essential component that is volatilized and functionsas a blowing agent during production of the silicone rubber sponge, aswell as giving fine, uniform cells. Component (D) must not undergoreactions, such as thermal decomposition or chemical reactions withother components, during production of the silicone rubber sponge, andmust be volatile at temperatures above room temperature. Examples ofcomponent (D) are water, aliphatic hydrocarbons such as n-pentane,n-hexane, isohexane, and cyclohexane; alcohols such as methanol,ethanol, and 1-propanol; ethers such as methoxy benzene andtetrahydrofuran; ketones such as acetone and methyl ethyl ketone; andlow-molecular weight siloxanes such as low-molecular weight lineardimethylsiloxanes and cyclic dimethylsiloxanes. Water and cyclicdimethylsiloxanes are preferred.

Component (D) is used in amounts of from 0.1 to 10 parts by weight per10 parts by weight of component (A). In excess of 10 weight parts ofcomponent (D) the cells of the sponge tend to become rough andnonuniform, while amounts less than 0.1 weight part do not givesufficient action as a blowing agent. To improve ease of handing andease of incorporation of component (D) it is permissible to add tocomponent (D) a thickener such as powdered silica, provided that theobjects of the invention are not impaired thereby.

Component (E), the curing agent, is an organic peroxide, or a platinumcatalyst and an organopolysiloxane containing silicon-bonded hydrogen.Examples of the former type, namely organic peroxides, include benzoylperoxide, t-butyl perbenzoate, o-methyl benzoyl peroxide, p-methylbenzoyl peroxide, m-methyl benzoyl peroxide, dicumyl peroxide, and2,5-dimethyl-2,5-di(t-butylperoxy)hexane. The amount of component (E) ispreferably 0.1 to 10 parts by weight per 100 parts by weight ofcomponent (A).

When component (E) is a platinum catalyst plus an organopolysiloxanecontaining silicon-bonded hydrogen, examples of the platinum catalystare finely divided platinum, platinum black, chloroplatinic acid,alcohol-modified chloroplatinic acid, chloroplatinic acid/olefincomplexes, chloroplatinic acid/alkenylsiloxane complexes, andchloroplatinic acid/divinyltetramethyldisiloxane complexes. In preferredpractice, the amount of component (E), expressed as metallic platinum,is from 0.1 to 500 ppm (weight basis) of the total composition.Organopolysiloxanes containing silicon-bonded hydrogen are crosslinkingagents and in the presence of platinum catalysts react with the alkenylgroups in component (A) to cure the present compositions. Examples oforganopolysiloxanes containing silicon bonded-hydrogen aremethylhydriopolysiloxane endblocked at both terminals withtrimethylsiloxy groups, a copolymer of methylhydriosiloxane anddimethylsiloxane endblocked at both terminals with trimethylsiloxygroups, a copolymer of methylhydriosiloxane and dimethylsiloxaneendblocked at both terminals with dimethylhydriosiloxy groups,tetramethyltetrahydriocyclotetrasiloxane, and the like. In preferredpractice, the amount of silicon-bonded hydrogen in component (E) will besuch that the molar ratio of silicon bonded-hydrogen in component (E) toalkenyl groups in component (A) is 0.5:1 to 10:1. Compounds known in theart as agents for regulating the catalytic activity of platinumcatalysts, such as 1-ethynyl-cyclohexanol, 3,-methyl-1-penten-3-ol, orbenzotriazole, may be added as well.

The present composition comprises components (A) to (E) describedhereinabove. Additives known in the art for inclusion in silicone rubbersponge compounds may be included as well, provided that the objects ofthe invention are not impaired thereby. Examples of such additivesinclude heat stability agents such as iron oxide, cerium oxide, andfatty acid cerium salts; flame retardants such as manganese carbonate,zinc carbonate, and fumed titanium dioxide; pigments such as red ironoxide, titanium dioxide, and carbon black; and silicone oils such asdimethylsilicone oil and methylphenylsilicone oil. The presentcomposition can be easily prepared by mixing components (A) to (E) plusany other ingredients that may be required. In preferred practice,component (A) is premixed with component (B) to produce a siliconerubber base compound, to which are then added components (C), (D), and(E). Examples of production equipment are kneader mixers, continuouskneader extruders, and other mixing or blending units.

Silicone rubber sponges may be produced from the present compositions byheating the composition to a temperature above the softening point ofthe thermoplastic resin of component (B) and curing. Silicone rubbersponges are formed by blowing and curing of compositions of theinvention. Silicone rubber sponges produced in this way have fine,uniform cells and excellent mechanical strength, making them useful asconstruction material airtight retaining gaskets, fire resistantgaskets, sealing materials, O-rings, and cushioning materials, as wellas sheath materials for rollers in copiers and the like.

EXAMPLES

A fuller understanding of the invention is provided through thefollowing examples. Proportions are expressed on a weight basis.Viscosity and Williams plasticity were measured at 25° C. Williamsplasticity was measured as follows. Williams plasticity was measured bya plasticity test in accordance with JIS K6249: 1997 “Testing methodsfor uncured and cured silicone rubber.” A tubular test piece (2 cm³volume) was prepared from silicone gum. The test piece was sandwichedbetween pieces of cellophane paper and placed in a parallel plateplastometer (WILLIAMS PLASTOMETER manufactured by Shimadzu Seisakusho)equipped with a dial gage. A 49 N load was applied, and after 2 minutesthe dial gage was read. Test piece thickness (mm) was recorded andmultiplied by 100 to give plasticity.

Reference Example 1

A silicone resin (softening point 80° C., specific gravity 1.20)composed of dimethylsiloxane units and methylphenylsiloxane units in a22:78 molar ratio was dissolved in dichloromethane, and the resultantsolution (solids content 30 wt %) was delivered at a rate of 100 cc/min.to a dynamic mixer together with pure water delivered at a rate of 25cc/min., where they were mixed to produce an aqueous dispersion. Using atwo fluid nozzle, the aqueous dispersion was sprayed continuously into aspray dryer with a hot nitrogen gas stream. The hot nitrogen gas streamtemperature was 70° C. and pressure was 0.05 MPa. The resultant hollowsilicone resin particles were immersed for 24 hours in an aqueoussolution consisting of 100 parts pure water and 1 part nonionicsurfactant (trimethylnonanol ethylene oxide adduct). Floating hollowsilicone resin particles were separated and collected. The hollowsilicone resin particles had an average particle size of 40 μm and shellwall average thickness of 4 μm and contained nitrogen gas enclosedtherein.

Reference Example 2

An acrylic resin with a softening point of 85° C. (trade name ELVACITE2008 manufactured by DuPont) was dissolved in dichloromethane and theresultant dichloromethane solution (solids content 10 wt %) wasdelivered at a rate of 100 cc/min. to a dynamic mixer together with purewater delivered at a rate of 25 cc/min., where they were mixed toproduce an aqueous dispersion. Using a two fluid nozzle, the dispersionwas sprayed continuously into a spray dryer with a hot nitrogen gasstream. The hot nitrogen gas stream temperature was 80° C. and pressurewas 0.025 MPa. The resultant hollow acrylic resin particles wereimmersed for 24 hours in an aqueous solution consisting of 100 partspure water and 1 part nonionic surfactant (trimethylnonanol ethyleneoxide adduct). Floating hollow acrylic resin particles were separatedand collected. The hollow acrylic resin particles had an averageparticle size of 20 μm and shell wall average thickness of 4 μm andcontained nitrogen gas enclosed therein.

Example 1

100 Parts of an organopolysiloxane gum (viscosity 20,000,000 mPa·s,Williams plasticity 160) composed of 99.6 mol % dimethylsiloxane unitsand 0.4 mol % methylvinylsiloxane units and endblocked at both terminalswith dimethylvinylsiloxy groups, 10 parts of a dimethylsiloxane oligomerendblocked at both terminals with silanol groups and having viscosity of60 mPa·s, and 40 parts of dry process silica with a specific surfacearea of 200 m²/g were charged to a kneader mixer and kneaded underheating until homogenous to prepare a silicone rubber base compound. To100 parts of the silicone rubber base compound were added 0.4 partp-methylbenzoyl peroxide, 0.5 part dicumyl peroxide, 1 part of thehollow silicone particles prepared in Reference Example 1, and 0.5 partdistilled water. The mixture was kneaded on a two-roll mill to produce asilicone rubber sponge composition. The composition was formed into asheet 3 mm thick which was then cured by heating in a 230° C. oven for10 minutes to produce a silicone rubber sponge sheet. The cells of thesilicone rubber sponge sheet were examined and found to be substantiallyuniform with an average cell diameter of 400 μm.

Example 2

The silicone rubber sponge composition of Example 1 was charged to a 65mmφ (φ=diameter) single screw extruder and extruded in a tube profile.The product was heated for 4 minutes in a 230° C. oven to produce asilicone rubber sponge tube. This silicone rubber sponge tube hadsubstantially uniform cells with an average cell diameter of 350 μm.

Example 3

16 cm³ of the silicone rubber sponge composition of Example 1 wascharged to a compression mold (32 cm³ cavity capacity) and heated for 15minutes at 170° C. to produce a silicone rubber sponge sheet. Thissilicone rubber sponge sheet nicely filled the mold and hadsubstantially uniform cells.

Example 4

100 Parts of an organopolysiloxane gum (viscosity 20,000,000 mPa·s,Williams plasticity 160) composed of 99.6 mol % dimethylsiloxane unitsand 0.4 mol % methylvinylsiloxane units and endblocked at both terminalswith dimethylvinylsiloxy groups, 5 parts of a dimethylsiloxane oligomerendblocked at both terminals with silanol groups and having viscosity of60 mPa·s, 15 parts of dry process silica with a specific surface area of200 m²/g, and 25 parts of wet process silica with a specific surfacearea of 130 m²/g were charged to a kneader mixer and kneaded underheating until homogenous to prepare a silicone rubber base compound. To100 parts of the resultant silicone rubber base compound were added 1part of a trimethylsiloxyl-endblockeddimethylsiloxane/methylhydriosiloxane copolymer (viscosity 25 mPa·s),0.002 part of 1-ethynyl-1-cyclohexanol (a hydrosilylation inhibitor), achloroplatinic acid/tetramethyldivinyl-disiloxane complex in an amountequivalent to 3 ppm (based on weight) as platinum atoms, based on theorganopolysiloxane gum weight, 0.5 part of the hollow acrylic resinparticles prepared in Reference Example 2, and 1 partoctamethylcyclotetrasiloxane. The mixture was kneaded on a two-roll millto produce a silicone rubber sponge composition. The composition wasformed into a sheet 3 mm thick which was then cured by heating in a 230°C. oven for 10 minutes to produce a silicone rubber sponge sheet. Thecells of the silicone rubber sponge sheet were examined and found to besubstantially uniform with an average cell diameter of 300 μm.

Example 5

The silicone rubber sponge composition of Example 4 was charged to a 65mmφ single screw extruder and extruded into a tube profile. The productwas heated for 5 minutes in a 230° C. oven to produce a silicone rubbersponge tube. This silicone rubber sponge tube had substantially uniformcells with an average cell diameter of 250 μm.

Example 6

16 cm³ of the silicone rubber sponge composition of Example 4 wascharged to a compression mold (32 cm³ cavity capacity) and heated for 20minutes at 170° C. to produce a silicone rubber sponge sheet. Thissilicone rubber sponge sheet nicely filled the mold and hadsubstantially uniform cells.

Example 7

The silicone rubber sponge composition prepared in Example 1 was coatedonto the outside of a roller core and set in a roller mold. Using acompression mold the silicone rubber sponge composition was cured byheating for 10 minutes at 170° C. to produce a silicone rubbersponge-sheathed roller. The cells of the silicone rubber sponge-sheathedroller were examined and found to be substantially uniform with anaverage cell diameter of 300 μm.

Example 8

The silicone rubber sponge composition prepared in Example 4 was coatedonto the outside of a roller core and set in a roller mold. Using acompression mold the silicone rubber sponge composition was cured byheating for 10 minutes at 170° C. to produce a silicone rubbersponge-sheathed roller. The cells of the silicone rubber sponge-sheathedroller were examined and found to be substantially uniform with anaverage cell diameter of 280 μm.

Comparative Example 1

A silicone rubber sponge composition was prepared as in Example 1, butomitting the hollow silicone resin particles used in Example 1. Thecomposition was formed into a sheet 3 mm thick which was then cured byheating in a 230° C. oven for 10 minutes to produce a silicone rubbersponge sheet. The silicone rubber sponge sheet had nonuniform cells,with some cells as large as 2500 μm in diameter.

Comparative Example 2

The silicone rubber sponge composition of Comparative Example 1 wascharged to a 65 mmφ single screw extruder and extruded into a tubeprofile. The product was heated for 5 minutes in a 230° C. oven toproduce a silicone rubber sponge tube. The cells were large andnonuniform, with some cells as large as 2500 μm in diameter.

Comparative Example 3

16 cm³ of the silicone rubber sponge composition of Comparative Example1 was charged to a compression mold (32 cm³ cavity capacity) and heatedfor 15 minutes at 170° C. to produce a silicone rubber sponge sheet.This silicone rubber sponge sheet did not fill the mold and hadnonuniform cells.

Comparative Example 4

A silicone rubber sponge composition was prepared as in Example 4, butomitting the hollow acrylic resin particles used in Example 4. Thecomposition was formed into a sheet 3 mm thick which was then cured byheating in a 230° C. oven for 10 minutes to produce a silicone rubbersponge sheet. The silicone rubber sponge sheet had nonuniform cells,with some cells as large as 2,000 μm in diameter.

Comparative Example 5

The silicone rubber sponge composition of Comparative Example 4 wascharged to a 65 mmφ single screw extruder and extruded into a tubeprofile. The product was heated for 5 minutes in a 230° C. oven toproduce a silicone rubber sponge tube. The cells were nonuniform, withsome cells as large as 1500 μm in diameter.

Comparative Example 6

16 cm³ of the silicone rubber sponge composition of Comparative Example4 was charged to a compression mold (32 cm³ cavity capacity) and heatedfor 15 minutes at 170° C. to produce a silicone rubber sponge sheet.While the silicone rubber sponge sheet filled the mold, its cells werenonuniform.

We claim:
 1. A silicone rubber sponge composition comprising (A) 100parts by weight organopolysiloxane gum described by average structuralunit R_(a)SiO_((4−a)/2), where R is a monovalent hydrocarbon group orhaloalkyl and a is 1.8 to 2.3 and having a viscosity of 1,000,000 mPa·sor above at 25° C., (B) 1 to 400 parts by weight inorganic filler, (C)0.01 to 50 parts by weight hollow thermoplastic resin particles, (D) 0.1to 10 parts by weight liquid blowing agent with a boiling point aboveroom temperature, and (E) a curing agent in an amount sufficient to curethe composition.
 2. The silicone rubber sponge composition according toclaim 1, where component (C) comprises thermoplastic resin shells havinga softening point of from 40° C. to 200° C. and having a gas enclosedtherein.
 3. The silicone rubber sponge composition according to claim 1,where the thermoplastic resin of component (C) is selected from thegroup consisting of silicone resin, acrylic resin, and polycarbonateresin.
 4. The silicone rubber sponge composition according to claim 1,where component (D) is water.
 5. The silicone rubber sponge compositionaccording to claim 1, where component (D) is adimethylcyclopolysiloxane.
 6. A silicone rubber sponge articlecomprising the reaction product of a composition comprising (A) 100parts by weight organopolysiloxane gum described by average structuralunit R_(a)SiO_((4−a)/2), where R is a monovalent hydrocarbon group orhaloalkyl and a is 1.8 to 2.3 and having a viscosity of 1,000,000 mPa·sor above at 25° C., (B) 1 to 400 parts by weight inorganic filler, (C)0.01 to 50 parts by weight hollow thermoplastic resin particles, (D) 0.1to 10 parts by weight liquid compound with a boiling point above roomtemperature, and (E) a curing agent in an amount sufficient to cure thecomposition.
 7. A silicone rubber sponge article according to claim 6prepared by a process selected from the group consisting of extrusionmolding and compression molding.
 8. A silicone rubber sponge articleaccording to claim 6, where the article is selected from the groupconsisting of a sheet, tube, gasket, and sheath material for a roller.9. The silicone rubber sponge composition according to claim 1, wherecomponent (A) has a viscosity at 25° C. of 5,000,000 mPa·s.
 10. Thesilicone rubber sponge composition according to claim 1 comprising ascomponent (B) 1 to 100 parts by weight of a reinforcing filler.
 11. Thesilicone rubber sponge composition according to claim 1, where component(C) has a softening point of from 60 to 180° C.
 12. The silicone rubbersponge composition according to claim 1, where component (C) has anaverage particle size within the range of 1 to 50 μm.
 13. The siliconerubber sponge composition according to claim 1, comprising 0.1 to 40parts by weight of component (C) per 100 parts by weight of component(A).
 14. The silicone rubber sponge composition according to claim 1,where component (E) is an organic peroxide.
 15. The silicone rubbersponge composition according to claim 1, where component (E) comprises aplatinum catalyst and an organopolysiloxane containing silicon-bondedhydrogen.